14 PFS 155C - 315C OM 135
Phase/Voltage Monitor
The phase/voltage monitor provides protection against three-phase electrical motor loss due to power
failure conditions, phase loss, and phase reversal. Whenever any of these conditions occur, a contact
opens which de-energizes the starter.
CAUTION
Incorrect phase rotation will damage the compressor.
When proper power is restored, contacts close and MicroTech enables compressors for operation.
When three-phase power has been applied, the output relay should close and the “run light” should
come on. If the output relay does not close, perform the following tests.
1. Check the voltages between L1 - L2, L1 - L3 and L2 - L3. These voltages should be approximately
equal and within +6% of the rated three-phase line-to-line voltage.
2. If these voltages are extremely low or widely unbalanced check the power system to determine the
cause of the problem.
3. If the voltages are good, using a phase tester, verify that phases are in A, B and C sequence for
L1, L2 and L3. Correct rotation is required for compressor operation. If required to do so by
phase sequence, turn off the power and interchange any two of the supply power leads at the
disconnect.
4. Turn on the power. The output relay should now close after the appropriate delay.
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